Can you accidentally bind people together via an object?

I Know a friend who is in a toxic relationship with his girlfriend however as clear as this is they cannot seem to break away from each other and he has inmesurable amounts of bad luck as well as she. This all sort of started ever since they made a blood necklace for each other -each carrying the other person's blood

That sounds like an accidental blood bind. Now, it doesn't necessarily have to be. If two average people did something like this, it's not guaranteed to have been affected by magick, as some people aren't as susceptible to spell-casting. People differ. It's why when someone performs a spell they may not be able to get it to work, while another person could get it to work every time. There's a certain level of energy manipulation that occurs. Accidental magick happens when someone is more free with their energy. This isn't a choice, obviously.
If this IS a binding…

Blood magick is used when you want something to be permanent. However, in reality, nothing can truly be permanent. There's things you could do to fix this, but since blood magick is so strong, it's gonna be a hell of a lot of work to break the bind. I'm not joking.
Whatever they did to make the necklaces, they should do the reverse of that. Cleanse at every step, before, after, and even during if they can. Each part of the necklace and blood should be disposed of. Bury each part for a while to sink them in, cleanse them, bury them again, cleanse them, and destroy them. If there is anything left when they're destroyed, by all means cleanse that, too.
Each person should destroy the necklace they, personally, made. Then cut any chords you can see if you can see auras/energy, etc. Whatever they can do and what they can try. Then there should be an unbinding spell completely separate with any material connections they can use.